Nutrients Abatement from digestate filtrate using Flow-Electrode capacitive Deionization: Role of carboxylate and...

Methanogenic digestate filtrate is rich in nutrients and organic ions, presenting a significant challenge for selective resource recovery. This study uncovers the role of carboxylates and amino acids in regulating nutrient recovery in flow electrode capacitive deionization (FCDI). Results revealed that increasing the influent bicarbonate from 200 to 2000 mg/L reduced NH₄⁺-N removal from 88.9 % to 72.5 %. The coexistence of acetate and bicarbonate suppressed nutrient removal by over 30.0 % via intensified ion competition and concentration polarization. The pH-dependent speciation of amino acids dictated their roles, with lysine acting as a cationic competitor below its isoelectric points (9.74) and anionic above. DFT calculations quantitatively validated the electrode's selectivity for phosphorus and amino acids (lysine: -0.707 eV > glutamic acid: -0.688 eV > glycine: -0.369 eV). These findings reveal ion-specific interactions governing FCDI performance, providing a mechanistic basis to optimize pH and feed composition for targeted nutrient recovery and amino acid valorization.